The present invention relates to a retrofit foundation system and specifically to a system for attaching the bottom portion of structure, such as a structure formed of a wood frame construction, to the foundation.
Before the introduction of seismic building codes, residential and small commercial structures were not required to have the bottom portion of the structure, commonly referred to as the sill plate, bolted to the concrete foundation. For example, in California, homes built before 1949 were not covered by any specific seismic building code, and even after that date many single family dwellings were exempt.
A problem which can occur with buildings which are not bolted to the foundation, and when there is seismic activity, is that the building structure may either move on the foundation or even slip off the foundation. Such movement of the building can thereby cause extensive damage to the building and injury to the occupants. Buildings that have been built after the seismic building codes were introduced, and which were not exempt, have solved these problems through anchor bolts positioned at regular intervals around the perimeter of the building and extending upward from the foundation and passing through complementary openings in the sill plate so as to have the ill plate bolted down to the concrete foundation.
Similarly, the preferred method in retrofitting older structures, which were built before the seismic codes or were exempt, is to add anchor bolts around the perimeter of the building and with the bolts parallel to the outside walls. This is the preferred method since the forces caused by seismic and wind activity are greatest around the perimeter of the building at the outside walls. The anchor bolts, which are either part of the original structure or are retrofit, are normally spaced every four (4) to six (6) feet on center around the perimeter of the building.
The difficulty is that many building structures have 2".times.6" joists resting directly on the sill plate to support the flooring for the first floor of the building. This means that there is a very small crawl space underneath the building and only a 6" space between the sill plate and the flooring. With this type of common building arrangement, it is very difficult to retrofit anchor bolts through the sill plate and down into the foundation because of the small spacing. In addition to the above, any other retrofit method of attaching the sill plate to the foundation must accommodate a number of other variations. These variations include the size of the sill plate varying from a nominal 2".times.4" to a full size 2".times.6", the width of the foundation wall varying from a minimum of 6" up to wider widths such as 8" wide and the positioning of the sill plate on the foundation wall.
There have been a number of prior art attempts to solve the problem of retrofitting an attachment between the sill plate, or other portion of the building construction, to the foundation. One attempt as described above, is to essentially duplicate that which is provided in new building construction. Specifically, anchor bolts are positioned every four (4) to six (6) feet on center around the perimeter and with the anchor bolts passing in an upward direction through the sill plate. In order to accomplish this, a right angle drill has to be used with special bits so as to drill down through the sill plate and into the foundation. The anchor bolts then have to be inserted through the sill plate and into the foundation and locked in place either with mechanical means or by adhesives such as epoxy.
A washer and nut would then be placed over the end of the bolt which protrudes from the sill plate and tightened down to lock the sill plate to the foundation. Although the above is an acceptable procedure, it is expensive and difficult to install and requires highly trained personnel to retrofit such anchor bolts. For example, it can take approximately 45 minutes to install each bolt, and it can be seen that such a period of time for each installed bolt can greatly increase the cost of retrofitting the bolting of the sill plate to the foundation.
Other prior art attempts that have been used include right angle plates and with a top part of the plate overlaying the sill plate and with a perpendicular part of the plate bolted to the concrete foundation. The top part of the plate, which overlays the sill plate, is nailed into position using special tooling and specifically a palm-nailer so as to properly nail the top part of the plate to the sill plate. Typically, palm-nailers are expensive and are normally driven by an air compressor so that it is necessary to drag air lines through the crawl space to drive the palm-nailer.
The major difficulty with the prior art right angle plate structure is strength. Specifically, the right angle plates can straighten out in response to forces moving perpendicular to an outside wall. In addition, there is no blocking against the right angle plate, and the nails driven through the right angle plate and into the top of the sill plate are the only restraint against the outside forces and can also tear up the sill plate. This type of right angle prior art device, therefore, is not as strong as anchor bolts and requires spacing from two (2) to three (3) feet on center to overcome the weaker nature of this type of device. This smaller spacing increases the cost of installation.
Another attempted solution to the retrofit problem is the use of a flat plate with custom blocking between the side of the sill plate and the edge of the foundation. The flat metal plate is then bolted to the side of the foundation and with long lag screws extending through the flat plate, the blocking material and into the sill plate. The difficulty with this type of prior art device is that every piece of blocking must be custom cut in the field to fit the specific distance from the side of the sill plate to the edge of the foundation since there is no standard distance between the side of the sill plate and the edge of the foundation.
Another difficulty with the flat plate device is that the blocking must either be glued or continuously nailed to the sill plate or another shear plane is created to act against the long lag screws. This greatly reduces the ability to transfer the load on the building down to the foundation. This flat plate prior art device, therefore, again, is not as strong as the anchor bolts used in new construction and this type of flat plate device is normally placed at every three (3) to four (4) feet on center, which increases the cost.
Another prior art device, which has been used, does not really address the issue of lateral shear since it is a hold down which resists uplift. This type of hold down device typically extends between the foundation and the joists which are mounted on the sill plate. This type of prior art device does not resolve the problem of retrofitting a frame construction building to resist seismic activity or high winds.
It should be noted that in all of the prior art attempts at retrofitting the locking of the building to the foundation, there does have to be some attachment between the concrete foundation and the frame construction of the building. This means that bolts have to be inserted into the foundation. This requires drilling into the foundation and the insertion and locking of bolts in position around the perimeter of the building. The drilling, insertion and locking of each bolt takes a considerable period of time. Therefore, any retrofit device should be as strong as possible so as to minimize the number of retrofit devices and thereby minimize the number of bolts which must be inserted into the concrete foundation.
For example, if new construction requires anchor bolts to be located every six (6) feet on center, then a retrofit system which requires that the bolts be located closer than six (6) feet on center is not desirable. For example, a retrofit system which requires devices to be two (2) to three (3) feet on center, such as with one prior art device or, three (3) to four (4) feet on center, as with another prior art device, require two (2) to three (3) times as much time and cost to install compared to a retrofit system which requires devices to be located approximately six (6) feet on center. The present invention is directed towards such a solution wherein the spacing of the retrofit devices is similar to new construction and which is easy to install and is relatively low in cost.